Flightline: 107 - Grumman X-29
The Grumman X-29 was built in the early 1980s to explore forward swept wings and new technologies and materials for aircraft construction.
In 1976 DARPA released a request for proposals for a forward swept wing (FSW) X-plane, and received three designs from General Dynamics, Grumman, and Rockwell. General Dynamics' design was a modified version of their F-16 fighter, while Grumman's Model 712 was partially based on the F-5, and the Rockwell Sabre Bat was partially based on the HiMAT RPV
Artist's impression of General Dynamics' F-16 FSW. | Illustration: General Dynamics
Concept art of the Grumman Model 712 with a thrust-vectoring nozzle. | Illustration: Grumman Aircraft
An armed variant of the Rockwell Sabre Bat shooting down a MiG. | Illustration: Rockwell International
Despite being a somewhat more advanced design (the wings were swept at 40° rather than the 33° of the G-712, and the seat was reclined for higher G loading), the Sabre Bat was rejected early in the program, leaving Grumman and General Dynamics. In 1981 the selection board chose the G-712, designating it as the X-29.
Orthograph of the Grumman X-29. | Photo: NASA Dryden FRC
Two X-29s were built, both of which were based on the forward fuselages of existing Northrop F-5A Freedom Fighters (63-8372 became 82-0003 and 65-10573 became 82-0049) to save on costs. Similarly, the control surface actuators and main landing gear were taken from F-16s. Forward swept wings, by their very design, experience a torsional effect which can. if unaddressed, twist the wings off. Previous FSW aircraft, composed of metal and wood, addressed this effect by being stiff and therefore heavy. Grumman, taking advantage of advances in materials, were fabricated from carbon fiber composites, which were specially layered to resist the torsion. The X-29 also featured canards forward and strake control surfaces alongside the engine. This configuration made the aircraft aerodynamically unstable, requiring constant computer control of the flight surfaces to keep it in flight. This instability however, coupled with the FSW, was anticipated to give the X-29 enhanced maneuvering capability. The X-29s flight control systems were equipped with three digital computers, along with three analog computers for redundancy. Any of the three could control the aircraft, and they would 'vote' on their measurements, allowing malfunction or erroneous data to be instantly recognized and isolated. The aircraft were powered by a GE F-404 engine fitted with an afterburner.
One of the X-29 aircraft prior to being painted. The contrast between the zinc chromate-painted metal portions and the carbon fiber wings is apparent. | Photo: Grumman Aircraft
The first X-29's maiden flight was on 14 December 1984 at Edwards AFB, and was turned over to NASA to begin its test program four months later. The following December, the X-29 went supersonic in level flight, the first FSW aircraft to do so. The 1st X-29 was not fitted with a spin recovery parachute, and so was limited in its test program, but it proved the basic theories were sound, and paved the way for the second aircraft to begin a more radical test program.
X-29 #1, registration number 82-0003, on display in 1986. | Photo: Wallace Shackleton
The second X-29 first flew on 23 May 1989, and was soon turned over to NASA for full scale testing. X-29-2 completed 120 flights, and demonstrated that the design allowed full control response at up to 45° angle of attack, and maintained limited control up to 67°. The program determined that less conservative limits on the flight control system and larger control surfaces would have allowed a higher degree of control at higher angles, but this has yet to be attempted on a full-scale demonstrator. After the end of its primary test program in 1991, the second X-29 participated in a USAF Vortex Flow Control test, which involved modifying the aircraft with two nitrogen tanks in the nose which fed into a pair of nozzles. These nozzles, it was hoped, would allow control of the aircraft at very high angles of attack when the rudder would lose effectiveness. During the 60 flights completed in 1992 demonstrated that the VFC was more effective than anticipated in affecting yaw, though it was not as effective against sideslip, and didn't counteract oscillation at all.
X-29-2 in flight in 1991. This particular flight was to help visualize airflow around the nose of the plane, hence the smoke generators in the nosecone. The deflection of the strake and wing control surfaces is also notable. | Photo: NASA DFRC
After the conclusion of their test programs, the two X-29s were retired, with X-29-1 going to the USAF Museum in Dayton, and X-29-2 being placed on display at the Armstrong Flight Research Center at Edwards AFB.
The first X-29 on display in the R&D Hangar of the National Museum of the USAF. | Photo: Valder137
X-29-2 on display at the Dryden (later Armstrong) FRC in 2009. | Photo: John Shupek